USE OF RADIOACTIVE SUBSTANCES AS FERTILIZERS. 5 



same as that given off from the preparation before the separation. 

 The total radiation has thus not been either increased or decreased 

 by the treatment, and as far as the use of the rays is concerned it 

 must necessarily be just as expensive, although possibly at times 

 more convenient, to treat plants with radium emanation as with the 

 radiation from the equilibrium amount of radium. 



THE INFLUENCE OF RADIOACTIVE RAYS ON PLANTS. 



Every physical agent known when exceeding a certain minimum 

 intensity is able to affect in a marked degree the germination of seeds 

 and the growth of plants. It would therefore be expected that the 

 rays from radioactive substances, when present in sufficient intensity, 

 would likewise have an influence on plant growth. A great many 

 experiments have been made along this line, and the literature on 

 the subject is already very extensive. Unfortunately in many of the 

 experiments which have been made, no mention is made of the 

 amount of radioactive material used nor of the intensity of the 

 radiations emitted by it. Consequently such experiments can not 

 be duplicated by others, and the results reported are therefore of 

 little value, for it could have been predicted that a very intense 

 radiation would have an injurious effect on plant growth, while ra- 

 diations of moderate intensity might exert a beneficial effect. Fur- 

 thermore, owing to an insufficient knowledge of the properties of 

 radioactive rays, many experiments have been carried out in such a 

 way that the effects which were attributed to the rays could not 

 possibly have been due to this influence. 



The most extensive experiments in this field which have been de- 

 scribed in this country were carried out by Gager x at the New York 

 Botanical Garden. In one set of pot experiments a quantity of 

 polonium (activity not given) inclosed in a sealed glass tube was in- 

 serted in the soil at the center of the pot, with the end containing the 

 radioactive material about 10 millimeters below the surface. Twelve 

 grains of wheat were then planted without soaking in the soil around 

 the tube. Three other pots were also prepared in the same way with 

 the same number of wheat grains; in one of the pots was placed a 

 tube containing 10 milligrams of radium bromide of 1,800,000 ac- 

 tivity; in another, a tube containing 10 milligrams of radium bro- 

 mide of 1,500,000 activity, while the remaining pot was used as a 

 control. On the fourth da} r measurements were made of the height of 

 the seedlings, and it was found that the average growth was greatest 

 in the pot containing the polonium and least in the control pot. It 

 is known, however, that polonium gives off alpha rays only, and that 

 these rays are so lacking in penetrating power that they could not 



1 Effects of the Rays of Radium on Plants, Memoirs of the N. Y. Botanical Garden, 

 vol. 4 (1908). 



